1. Field of the Invention
The present invention relates to an organic electroluminescence display, and more particularly, to an organic electroluminescence display and a fabricating method thereof enabling to simplify a fabricating process by forming a single insulating layer pattern having functions of an insulating layer and barrier ribs, upgrade an image quality by increasing an aperture ratio, and reduce a product cost.
2. Background of the Related Art
Generally, an organic electroluminescence (hereinafter abbreviated EL) display is one of flat panel displays, includes an organic EL layer inserted between anode and cathode layers on a substrate so as to be thin, and can be formed like a matrix type. Different from a plasma display panel(PDP) as another emissive display requiring a high driving voltage over 200V, the organic EL display as an emissive display can be driven by a low voltage below 15V so as to be suitable for a portable device. Compared to TFT-LCD as a non-emissive display, the organic EL display has higher brightness and wider viewing angle as well as more excellent characteristics such as a response time below about 1 μsec and the like. Specifically, the organic EL display has the response time more excellent than those of other flat panel displays, thereby being very suitable for an IMT-2000 mobile phone to which a function of moving pictures is essential.
Yet, since an organic EL layer and a cathode layer of such an organic EL display are vulnerable to oxygen and moisture, surroundings of a fabrication process should be made airtight in order to secure a reliability of the organic EL display. Hence, the fabrication process is unable in general to use photolithography for pixellation or patterning.
Therefore, pixellation of organic and cathode layers of the organic EL display uses direct pixellation using a shadow mask instead of photolithography including masking/etching processes exposed to oxygen and moisture. Yet, such a method is inadaptable to use if a pitch between pixels, i.e. an interval between lines of the organic and cathode layers, is reduced so as to realize high resolution.
There is another method of patterning the organic EL display, which is carried out in a manner that a cathode layer is patterned using a separator after an insulating layer and a separator have been formed with an electrically insulating material on an anode layer and a substrate.
In this case, the insulating layer is formed on an entire area except a dot-like opening area of the anode layer. The insulating layer defines pixels, inhibits leakage current from edges of the cathode, and prevents the cathode and anode layers from being short-circuited at a boundary between the cathode and anode layers since the stacked organic layer becomes thinner near the separator due to a shadow effect by the separator in a direction vertical to the anode layer formed for patterning of the cathode layer.
The separator formed on the insulating layer crosses with the anode layer to be arranged so as to leave an interval from each other as well as has an overhang structure so as not to make the cathode layer be short-circuited with an adjacent component. Specifically, unlike a general patterning process, a negative profile should be maintained in order to prevent short-circuit between adjacent cathode layer lines. If the separator is missing, there is a chance to be short-circuited with an adjacent pixel.
In order to fabricate the organic EL display stably, both of the insulating layer and separator are necessary. Yet, each process requires photolithography, thereby becoming complicated as well as increasing a product cost of the organic EL display.
A method of fabricating an organic EL display according to a related art is explained in detail by referring to the attached drawings as follows.
FIGS. 1A to 1C illustrate layouts of an organic EL display according to a related art.
Referring to FIG. 1A, a plurality of first electrodes 2 formed of ITO(indium tin oxide) or the like are arranged like a stripe type on a transparent substrate 1.
Referring to FIG. 1B, a lattice type insulating layer pattern 3 is stacked on the first electrodes 2 and transparent substrate 1 in an area between the first electrodes 1 and an area crossing with the first electrodes 2 except dot-like openings on the first electrodes 2.
Referring to FIG. 1C, separators 4 are formed on the insulating layer pattern 3 between the dot-like openings so as to cross with the first electrodes 2. Although not shown in the drawing, an organic EL layer and second electrodes(cathode layer) are stacked on the first electrodes 2 including the insulating layer pattern 3 and separators 4.
FIGS. 2A to 2C illustrate cross-sectional views of a method of fabricating an organic EL display along cutting lines A-A′ in FIGS. 1A to 1C according to a related art.
Referring to FIG. 2A, an anode layer(not shown in the drawing) formed of ITO(indium tin oxide) or the like is stacked with a predetermined thickness on a transparent substrate 1 by sputtering. A photoresist layer(not shown in the drawing) is coated on the entirely-deposited anode layer. Exposure and development are carried out on the photoresist layer using a mask so as to form a stripe type photoresist pattern(not shown in the drawing). The entirely-deposited anode layer is etched using the photoresist pattern. And, the photoresist pattern is removed so as to form stripe type patterns of first electrodes 2.
Referring to FIG. 2B, an insulating layer(not shown in the drawing) is stacked for electric insulation on the transparent substrate 1 including the first electrodes 2. The insulating layer can be formed with organic or inorganic material. The organic material uses resin or photoresist including acrylic-, novolac-, or epoxy-based material. And, the inorganic material uses silicon oxide, silicon nitride, silicon oxinitride, or the like. The insulating layer is patterned so as to form a lattice type insulating layer pattern 3 on the first electrodes 2 and transparent substrate 1 except the dot-like openings formed on the first electrodes 2.
Referring to FIG. 2C, a negative type organic photoresist layer(not shown in the drawing) is stacked on the insulating layer pattern 3 using an electrically insulating material, and then a patterning process is carried out so as to form separators 4 having a negative profile. In this case, the separators 4 are arranged on the insulating layer pattern 3 between the dot-like openings so as to cross with the first electrodes 2, and has an overhang structure so as to prevent second electrodes 6 from being short-circuited with adjacent components. And, an organic EL layer 5 and second electrodes 6 are stacked in order using a shadow mask(not shown in the drawing).
In order to protect the organic EL layer and second electrodes(cathode layer) and the like vulnerable to moisture and oxygen, an encapsulation layer formed of metal, glass, or the like or a passivation layer formed of inorganic or organic material is formed on an entire surface including the second electrodes 6 so as to make the organic EL display airtight from outside.
FIGS. 3A to 3C illustrate cross-sectional views of a method of fabricating an organic EL display along cutting lines B-B′ in FIGS. 1A to 1C according to a related art.
FIGS. 4A to 4C illustrate layouts of an organic EL display according to another related art.
Referring to FIG. 4A, a plurality of first electrodes 2 formed of ITO(indium tin oxide) or the like are arranged like a stripe type on a transparent substrate 1.
Referring to FIG. 4B, a stripe type insulating layer pattern 3 is stacked on the transparent substrate 1 and an area crossing with the first electrodes 2 on the first electrodes 2.
Referring to FIG. 4C, a photoresist layer 7 is formed on the transparent substrate 1 including the first electrodes 2 and insulating layer pattern 3. The photoresist layer 7 fails to cover openings 8 exposing the first electrodes 2 and middle portions of the insulating layer pattern 3 in the same direction of the insulating layer pattern 3. Trenches 9 are then formed by etching the exposed middle portions of the insulating layer pattern 3 with a predetermined thickness. Thus, the photoresist layer 7 exposes the openings on the first electrodes 2 so as to construct a lattice shape overall. An organic EL layer formed on the first electrodes 2 including the openings 8 and second electrodes(cathode layer) are not shown in the drawing.
FIGS. 5A to 5C illustrate cross-sectional views of a method of fabricating an organic EL display along cutting lines A-A′ in FIGS. 4A to 4C according to another related art.
Referring to FIG. 5A, an anode layer(no t shown in the drawing) formed of ITO(indium tin oxide) or the like is stacked with a predetermined thickness on a transparent substrate 1 by sputtering. A photoresist layer(not shown in the drawing) is coated on the entirely-deposited anode layer. Exposure and development are carried out on the photoresist layer using a mask so as to form a stripe type photoresist pattern (not shown in the drawing). The anode layer is etched using the photoresist pattern. And, the photoresist pattern is removed so as to form stripe type patterns of first electrodes 2.
An insulating layer(not shown in the drawing) is stacked for electric insulation on the transparent substrate 1 including the first electrodes 2. The insulating layer is formed with silicon oxide, silicon nitride, silicon oxinitride, or the like by vacuum deposition such as sputtering, chemical vapor deposition, or the like. The insulating layer is patterned by photolithography so as to form insulating layer patterns 3, which are arranged to leave an interval from each other so as to cross with a plurality of the first electrodes 2.
Referring to FIG. 5B, a positive type photoresist layer 7 is stacked on the insulating layer patterns 3 using an electrically insulating material, and then exposure and development are carried out on the photoresist layer 7 so as to form openings exposing the first electrodes 2 as well as expose middle portions of the insulating patterns 3 in parallel with the insulating patterns 3, respectively.
Referring to FIG. 5C, trenches 9 are formed by etching the middle portions of the insulating patterns 3 using the patterned photoresist layer 7, respectively. A cross-section of each of the trenches 9 looks rectangular. Yet, the cross-section is a trapezoid or a half-circle. And, the structure of the trench 9 prevents short-circuit between the adjacent second electrodes(cathode layer).
And, an organic EL layer(not shown in the drawing) and second electrodes(not shown in the drawing) are stacked in order.
In order to protect the organic EL layer and second electrodes(cathode layer) and the like vulnerable to moisture and oxygen, an encapsulation layer formed of metal, glass, or the like or a passivation layer formed of inorganic or organic material is formed on an entire surface including the second electrodes so as to be isolated from outside.
Unfortunately, the method of fabricating the organic EL display according to the related art has the following problems or disadvantages.
The patterns of the insulating layer define pixels, inhibit leakage current from edges of the cathode, and prevent the cathode and anode layers from being short-circuited at a boundary between the cathode and anode layers since the stacked organic layer becomes thinner near the separator due to a shadow effect by the separator in a direction vertical to the anode layer formed for patterning of the cathode layer. The separator formed on the insulating layer crosses with the anode layer to be arranged so as to leave an interval from each other as well as has an overhang structure so as not to make the cathode layer be short-circuited with an adjacent component. Specifically, unlike a general patterning process, a negative profile should be maintained in order to prevent short-circuit between adjacent cathode layer lines. In order to fabricate the organic EL display stably, both of the insulating layer and separator are necessary. Yet, each process requires photolithography, thereby being complicated as well as increasing a product cost of the organic EL display.